Such a headrest device is disclosed in JP2001-314268A, JP2003-79474A and JP2004-202062A.
JP2001-314268A discloses a headrest device in which a headrest is mounted in the middle of an upper lateral rod of a backrest support frame. The headrest is not so strongly supported and each side is unstable.
JP2003-79474A discloses a headrest device in which a headrest is mounted to a headrest rod projecting from the backrest, and JP2004-202062A discloses a headrest device in which a headrest frame is supported in the middle of a backrest support frame to move up and down, a headrest being mounted in the middle at the upper end of the headrest frame. But in both of the headrest devices, when the headrest moves up away from the backrest support frame, a support strength is not sufficient and the headrest and support therefore+ are likely to be unstable.
In an elevating member for supporting the headrest in the headrest device in JP2003-79474A, C-like sectioned engagement grooves of right and left ends engage with right and left side rods of a headrest frame, and an engagement projection on the side rod selectively engages in the engagement groove allowing the headrest so that the headrest may move up and down. For mounting the elevating member, the side rods of the headrest frame have to be elastically changed in shape outward and sideward by a strong force to increase a gap between opposing surfaces to make mounting troublesome.
When the headrest moves up and down, the elevating member is pressed and pulled up and down by strong forces. It is necessary to engage an engagement projection in a groove by expanding the headrest frame elastically. It would be very difficult to move the headrest up and down easily. Also the engagement projection strongly rubs against the groove to cause wear and loosening.
A plurality of engagement grooves is formed in a hole, for which a lateral rod is required. The elevating member becomes larger. So appearance becomes poor and it would be very difficult to design the elevating member itself and the headrest device freely.